Defect Engineering in A 2 BO 4 Thin Films via Surface-Reconstructed LaSrAlO 4 Substrates.

Ruddlesden-Popper oxides (A 2 BO 4 ) have attracted significant attention regarding their potential application in novel electronic and energy devices. However, practical uses of A 2 BO 4 thin films have been limited by extended defects such as out-of-phase boundaries (OPBs). OPBs disrupt the layered structure of A 2 BO 4 , which restricts functionality. OPBs are ubiquitous in A 2 BO 4 thin films but inhomogeneous interfaces make them difficult to suppress. Here, OPBs in A 2 BO 4 thin films are suppressed using a novel method to control the substrate surface termination. To demonstrate the technique, epitaxial thin films of cuprate superconductor La 2- x Sr x CuO 4 (x = 0.15) are grown on surface-reconstructed LaSrAlO 4 substrates, which are terminated with self-limited perovskite double layers. To date, La 2- x Sr x CuO 4 thin films are grown on LaSrAlO 4 substrates with mixed-termination and exhibit multiple interfacial structures resulting in many OPBs. In contrast, La 2- x Sr x CuO 4 thin films grown on surface-reconstructed LaSrAlO 4 substrates energetically favor only one interfacial structure, thus inhibiting OPB formation. OPB-suppressed La 2- x Sr x CuO 4 thin films exhibit significantly enhanced superconducting properties compared with OPB-containing La 2- x Sr x CuO 4 thin films. Defect engineering in A 2 BO 4 thin films will allow for the elimination of various types of defects in other complex oxides and facilitate next-generation quantum device applications.